It is, of course, well known to prepare organic thermoplastic polyurethanes by the reaction of organic diisocyanates with polymeric diols and diol chain extenders. It is also known to prepare water-dispersed polyurethane polymers. U.S. Pat. No. 3,479,310, for example, discloses water-dispersed plastics, which, as a latex, are suitable for the preparation of waterproof coatings. These plastics are prepared from polyhydroxy compounds, organic polyisocyantes, chain lengthening agents, if desired, and a sufficient amount of a component having an ionic salt-type group.
U.S. Pat. Nos. 3,905,929 and 3,920,598 disclose water-dispersible polyurethanes having side chain polyoxyethylene units, and U.S. Pat. Nos. 4,028,313 and 4,092,286 disclose water-dispersible polyurethanes having both an ionic salt-type group and side chain polyoxyethylene units.
However, even though aqueous compositions of dispersed polyurethanes are described, there is no teaching in any of these references of polyurethanes which are suitable for preparation of polyurethane coatings which can be subsequently dispersed by water or an aqueous organic solvent.
U.S. Pat. No. 4,110,284 discloses the preparation of ionic group-containing polyurethane latexes by the reaction of a hydrophilic polyester or polyether with an organic polyisocyanate. The patent does not disclose polyurethanes that can be coated onto a substrate and subsequently redispersed in water or aqueous organic solvents.
The linear polyurethanes of my invention can be used as protective coatings, primers, binders, etc.